I've never seen anyone make a TNT canon.
It is actually a necessary skill to raid certain types of campers. I have used one to raid a camper on the map garden with great success. He built an extremely large glass wall to block enderpearls, but I was able to blow it up all the way from mid.
Who plays on teams without a teammate? I'd just leave if I didn't have a teammate.
Actually, it is unwise to just leave if you do not have teammates. Even without much skill, it is still possible to win without a teammate. I have done so many times, on maps with 3 and 4 players per team. I had no teammates from start to end.